1. Field of the Invention
The present invention relates to an envelope generating apparatus of a musical tone generating apparatus used for a keyboard, an electronic piano, a synthesizer, etc. More specifically, the present invention pertains to an envelope generating apparatus which generates a complicated envelope.
2. Description of the Related Art
Conventionally, the dynamic level of a musical tone generated by an electronic musical instrument is realized by adding an envelope to tone wave data which is read from a wave memory.
In other words, a tone wave data signal read from the wave memory is multiplied by an envelope signal generated by an envelope generating apparatus to generate a tone signal of a predetermined timbre having a dynamic level.
In general, an envelope signal has multiple phases, such as attack, decay and release. The envelope generating apparatus, therefore, generates an envelope signal for each phase.
Two parameters are used to generate an envelope signal for each phase. One parameter is "target level LV" specifying a target value (level), and the other is "envelope speed parameter SP" specifying a time required for the level to reach the target value.
The envelope generating apparatus generates an envelope signal of a predetermined phase, for example, by repeating the following operation: the envelope generating apparatus holds the current value of an envelope to be generated, multiplies the envelope speed parameter SP by the difference between the target level LV and the current value, and adds the result to the current value.
To generate an envelope signal having three phases, attack, decay and release, parameters of the target level LV and envelope speed parameter SP should be prepared in advance, and when a request to generate the envelope signal made, the above-described operation should repeatedly be executed for the individual phases, attack, decay and release, using the prepared parameters.
The envelope signal generated in this manner is multiplied by tone wave data which is read from the wave memory, yielding an envelope-added musical tone.
The conventional envelope generating apparatus as described above, therefore, cannot generate a complicated envelope signal which has multiple phases.